In a production assembly line, circuit boards are conventionally transported on conveyors through assembly processes such as solder stenciling or reflow soldering. Typically, these conveyors are parallel tracks with regularly spaced supports distributed along a flexible member, such as a chain, for supporting the circuit boards. However, to accommodate circuit boards having different widths, the parallel tracks need adjustments which increases overall production time. Production time is further increased because circuit boards of one width have to be completely conveyed through the conveyor before such adjustments can be made to accommodate circuit boards of another width.
During conveyance, factors such as levelness and stability are important for component mounting. For example, when components are held by molten solder during reflow soldering, tilting or inadvertently shaking the boards can cause components to be displaced from their desired mounting positions.
Conveyors known in the art include U.S. Pat. No. 4,759,436 which discloses a conveyor with adjustable supports for conveying objects along a curved path which could also be applied to objects having different widths. The supports are pivotal about a horizontal axis to accommodate movement of a free end to support the objects. Unfortunately, the movement of the free end can cause tilting of objects such as circuit boards. Also known in the art is U.S. Pat. No. 4,840,268 which discloses an adjustable width chain conveyor with inner plates and adjustably sliding on inclined portions. Movement of the conveyor within guide rails allows for small variations in widths of circuit boards being conveyed. In conveying circuit boards having different widths, height of the circuit boards above a ground plane also varies. The inner plates, however, obstructs conventional overhead solder stenciling or reflow heat for soldering components. In addition, the sliding of the chain along the inclined portions may not be equal on both sides and, therefore, the circuit boards may tilt during conveyance. Both conveyors described above are also of a size that is inappropriate for use within conventional reflow ovens which typically have limited vertical spaces. Furthermore, contact with the adjustable supports or the inner plates when loading circuit boards onto the conveyors can cause an impact of a sufficient strength to displace unsoldered components. Hence, these conveyors are not suitable for use when solder stenciling or reflowing circuit boards.
It is desirable, therefore, for conveyors to be effective in conveying circuit boards having different widths through assembly processes such as solder stenciling and reflow soldering.